Inappropriate constancy scaling
The illusion contains perspective cues that increase the perceived size of more distant objects e.g. an equilateral triangle might be perceived as the flat picture of a road seen in perspective, with the top apex lying at infinity and the bottom base as the nearest part of the road.²
The trick is that this theory doesn’t explain the Triangle-bisection illusion. On the contrary, it works in the opposite direction. In the case of road in perspective, a spot halfway up the triangle would look more than half way down. (While in the YouTube example it looks more than halfway up).
“However, we do not believe that constancy scaling operates in the triangle-bisection illusion because the perceived effects are in the wrong direction.” — Anstis, S., Gregory, R. and Heard, P. (2009). The Triangle-Bisection Illusion. Perception, 38(3), p.330.